1. Field of the Invention
The present invention relates to a speaker apparatus. In particular, the present invention relates to a flat-panel speaker apparatus. The speaker apparatus of the present invention can be applied also to a spherical speaker apparatus.
2. Description of the Related Art
A technique regarding a conventional speaker apparatus, a technique for reproducing a recorded signal by using a plurality of speaker apparatuses and using case of a small speaker apparatus in a computer system will be described in the following.
First, the technique regarding a speaker apparatus will be described. In addition to a cone-shaped speaker apparatus, a flat-panel speaker apparatus using a flat diaphragm have come into general use as a speaker apparatus. FIG. 10 shows a flat-panel speaker apparatus of the prior art. In FIG. 10, numeral 1010 denotes a diaphragm, numeral 1020 denotes a transducer, and numeral 1030 denotes a listener. For convenience in a description, a frame for supporting the diaphragm, etc. is omitted in FIG. 10. An input signal Vin is an electric signal as a sound signal, and is an analog signal. If an original source of sound information is provided as a digital signal, it is converted into an analog signal by means of a D/A (digital-analog) conversion, so as to obtain the input signal Vin. The input signal Vin is inputted to the transducer 1020. The transducer 1020 converts the electric signal as the sound signal into mechanical vibration. The transducer 1020 is attached to the diaphragm 1010, which converts the mechanical vibration from the transducer 1020 into a sound signal.
Amplitude spectrum and sound pressure of an output signal are important in a speaker apparatus. In other words, for reproducing various kinds of tones, it is preferable that the amplitude spectrum of the output signal is flat in a wide band range, and for reproducing a powerful signal, it is preferable that the sound pressure of the output signal is large. In the conventional speaker apparatus described above, by considering and adjusting a diaphragm material, the ratio of length and breadth of the diaphragm, a method for attaching the diaphragm to the frame and a method for attaching the transducer to the diaphragm, an almost flat amplitude spectrum can be achieved in a wide band range. On the other hand, for larger sound pressure of the output signal, there have been techniques in which the vibration capability of the transducer 1020 is enhanced to increase the vibration of the diaphragm 1010, and a plurality of transducers 1020 are attached to a single diaphragm 1010 in parallel so that the same signals are distributed and inputted to these transducers 1020.
Next, the technique for reproducing the recorded signal by using a plurality of the speaker apparatuses will be described.
FIGS. 11 and 12 illustrate concepts of recording and reproducing a signal. FIG. 11 illustrates the concept during recording, with numeral 1060 denoting a sound source, numeral 1070 denoting a virtual boundary, numeral 1040 denoting microphones and numeral 1030 denoting a listener. The virtual boundary 1070 is provided virtually for objectively defining a signal propagating from the sound source 1060 to the listener 1030. The signal outputted from the sound source 1060 passes through the virtual boundary 1070, so that the listener 1030 listens to this signal. It is ideal that all the sound passing through this virtual boundary 1070 is recorded, but from a viewpoint for practice, a plurality of the microphones 1040 are arranged on the virtual boundary 1070 for recording.
In the prior art, it is possible that the sound signal that has been recorded stereophonically is processed focusing on a phase difference, thereby estimating and synthesizing a sound passing through the other arbitrary points on the virtual boundary 1070.
FIG. 12 illustrates the concept of the ideal signal reproducing. Numeral 1050 denotes speaker apparatus. As is clear by comparing FIG. 12 with FIG. 11, each of the speaker apparatuses 1050 is arranged in a position corresponding to that of the microphone 1040 used for recording. A sound signal that has been recorded by the corresponding microphone 1040 is supplied to each of these speaker apparatuses 1050 as an input signal, and then is reproduced, so that a situation of recording the sound source can be reproduced precisely, achieving the ideal signal reproducing for the listener 1030.
Although there are five microphones 1040 and five speaker apparatus 1050 in FIGS. 11 and 12, these numbers are for convenience in description and not limited to five.
Next, a speaker wall (a speaker array) in which many speaker apparatuses are arranged on a wall surface as shown in FIG. 13 for achieving better signal reproducing is known in the prior art. In principle, this is configured by arranging many speaker apparatus shown in FIG. 12 on the wall surface. Ideally, a large wall surface is preferable for achieving a powerful sound in this speaker wall, while the speaker arrays in which many small speaker apparatuses are integrated so as to achieve a portable size also have been under development.
Next, the form of utilizing the small speaker apparatuses in the computer apparatus will be described.
Accompanying the recent development of multimedia technology in a computer apparatus, speaker apparatuses are utilized as a sound output device. The speaker apparatuses are arranged in such a manner that small speaker apparatuses are arranged externally on both sides of a control apparatus casing or inside the same.
The above-described speaker apparatus of the prior art have had the following problems.
First, in general, the listener arranges the speaker apparatuses in a room of various sizes and shapes, and recording is conducted in various situations, making it difficult to arrange a necessary number of speaker apparatus in the ideal positions shown in FIG. 12. Therefore, a voice that has been recorded in one environment has to be reproduced with a speaker located in the position other than a predetermined position. Consequently, a reproduced sound becomes different from the sound that should be obtained by reproducing a recorded sound properly.
Second, the speaker wall extending over the entire wall surface as shown in FIG. 13 is very expensive. Also, it is difficult to construct a speaker wall for a special purpose on a wall surface of a room inside an ordinary house. Thus, the speaker walls are not widespread very much.
Next, because the small speaker array is constituted by integrating small speaker apparatuses, the individual speaker apparatus that outputs signals is small, so that the size and area of the diaphragm of the speaker apparatus also are small. The small size of the diaphragm causes a lack of reproducing capability in a low sound frequency range with a long wavelength, and the small area of the diaphragm causes the output signal to have small sound pressure. In addition, since the small speaker apparatuses are integrated, the cost increases.
In addition, when the speaker apparatus is combined with the computer apparatus, a problem arises in both cases of external and internal arrangements. That is, in the case of the external speaker apparatus, limitation in a peripheral installation space of the computer apparatus often makes it difficult to install the speaker apparatus. On the other hand, in the case of internal speaker apparatus, the relationship with the other components in the computer apparatus casing makes it difficult to secure a sufficient loading space for the speaker, leading to the speaker apparatus having a small diaphragm, which has low reproducing capability in a low sound range and outputs sound with a small sound pressure.